Shruthi Filterboard smr4mkII doesn't work

I have soldered my first Mutable Instrument over X-mas. It was not my first project and i can solder - I think :slight_smile:

The digital board works very fine. But if i try to change the cutoff and stuff nothing is happend. There is on every point on the board i should check the same raw signal from the digi-board.

I think there are no cold solderpoints and the Parts are in correct position.

Further: If i switch oszillator 1 and 2 to “none” there is no Signal on the Outputjack, if i play a note but on the Input-jack. One Pin of the IC2 wasn’t soldered at the first test of the shruthi but i have found the problem quick. but still there is no filtering.

Could you tell me where fail on the Board is? Which part could i have maybe destroyed?

thank you and greetings from Germany

hello Uli,
did you go tru the trouble shooting guide on this page ? Especialy step 5? power supply testing?
How are you testing? Do you have the 2 boards fully connected?
What signal is on the input jack?

Also, what is the voltage on IC4 pin 7 when cutoff = 0 ; and when cutoff = 127 (Just making sure that the filter is “closing” properly rather than being opened all the time).?

On the inputjack is the Signal you should hear if you make the two oscillators “none” and play a note…

i will test the Power Signal in the evening again…

It is normal that the IC of the power supply is getting hot?

It sounds like IC1 is fried. Test the -5v rail. I had a unit stop outputting but the digital board worked. Same behavior were audio would come out of the input only. I found that the 1054 was bad. Swapped it and it came back to life. Make sure there are no shorts around the power supply.

FYI, the 1054 was just a dud. I didn’t have any shorts anywhere. It happens sometimes.

Yes, it is normal that the 7805 gets hot.

One thing I am not sure about… do you get the same signal as the “OSC>” point throughout all the test points on the filter board (with more or less the same loudness)? Or something else?